My current ebike has a steel frame, front hub motor, rear battery pack (36V x 12AHr), front and rear racks, internally geared rear hub and suspension seat. All that and few things like a lock and small tool kit makes it tip the scales between 60 and 75 pounds. It works well as grocery getter and running my few errands but I would to put something together that is a tad bit lighter. My profound ignorance complicates the task thus I am requesting comments, thoughts and/or suggestions.

I live in Houston, Texas. That means that the terrain is 95% flat. To get a change in elevation of 150 feet would require crossing an Interstate via an overpass or riding up a number of levels in a parking garage. The other relative point is that the street pavement is bloody awful and sidewalks are worse. So skinny, high pressure tires are not an option. Lastly it would be at least 50 mile round trip ride to get to anything that resembles woods, forest or dirt trails. So this bike is strictly an urban hybrid.

The idea is to build something light weight, but still full size and reliable that can be ridden either as a short range ebike or normal urban hybrid without paying a severe penalty for including the motor assist. I am going to set a ridiculous target of under 30 pounds (13.6 KG).

I happen to have acquired a stripped 54cm 1989 Miyata CT-7000 frame and fork. This is a carbon-fiber/aluminum composite frame with a aluminum fork that weights just under four founds (1.8 Kg). I have been looking at building a rear wheel with a light weight geared hub motor. It seems that QT75 and 85 are in short supply so at this point I am considering a QT100 (4.6 pounds = 2.1 Kg plus controller). My understanding is that these motors have almost no drag when not powered. However they do require a 36 spoke wheel. The range of 36 spoke, rim brake wheels designed to mount 700Cx32-40mm tires is somewhat limited (and heavy). In the 650C range they are almost non-existent (I did locate some 450 gram Alex Assault Rims on Ebay but they have 13.5 grip width). However being realistic I am not likely to save more that one pound (2.2 KG) with the lighter Rims and spokes. Thus I am considering Sun Ryno Lites (0.565 KG/each).

However the though occurs to me: just how much of weigh penalty would be involved in using a 36 volt Bafang Mid Drive. I have not seen any accurate weights for the drive system. It also includes the Crank, Bottom Bracket and Motor controller. Thus the weight of all these items would be offset as well. This would also open up the range of rims that could be used not to mention the advantage of the motor operating through the gear train. I have also not seem to remember (or forgotten) how much drag the bafang mid drive adds if the motor is not powered. Can someone comment on their experience in this regard?

Well perhaps a question. Why exactly is the weight of your bike a problem? Do you need to carry it up stairs, or load it on a bike rack? Do you need a lighter bike, or do you just want to build a bike? Build many bikes if the desire comes to you. It's fun!

What I'm trying to say is, riding around a sprawling city like Houston, I'd think going the other way some might be worth it. Longtail bike, able to easily carry longer range battery, and or more cargo back from the grocery. My current version of this weighs in about 100 pounds with a 700 wh battery aboard.

Of course, I'm obviously now a complete convert to the long bike idea. The comfort level of them is so much better than short bikes, and to really replace a car you do need to be able to carry more. But they do suck if you have to carry the bike!

Of course a light bike such as you have does have it's place. Ideal if you have a short commute you do often enough.

5 mile round trip to school or work, something like that. Or the last mile thing, where you put the bike on a bus or in a car for some of the trip. Like you bike to your ride share meeting place, or ride share and then bike the last few miles to your destination. Or maybe you need to fit the bike into a closet once at work, or some other small space.

Anyway, I'd be tempted to just make that frame into a very light single speed and just pedal it. In season I mean. Not in the afternoon for the next few months. Oddly enough, I actually have more pedal bikes on the property than e bikes. Hard to believe for a guy like me.

I no longer maintain a four wheel vehicle so there is no danger of needing to load it in a car (because of the cost of insurance, maintenance, taxes, etc). However there are these municipal buses with bike racks on the front bumper Otherwise most of trips are under five miles.

Velocity makes some 700C rims in 36 hole. Off the top of my head, The Dyad comes in at 560grams, and is built for tandems, so its extra strong. The Aileron is a Disk rim, but come in at 460 grams. I think there are others, as well. You'll find even more 36 hole rims if you look for 29er rims.

BMSbattery used to sell the 108 in a 32 spoke hole version, but not no more.

John in CR wrote:If I was going weight weenie, I'd seriously consider going with the Maxwell EPO that member Grindz is involved with http://endless-sphere.com/forums/viewtopic.php?f=3&t=70440. There's room left in the triangle for a long range extender pack with enough capacity to get anywhere in Houston.

What you really need though is a 2nd high power and speed moped with good aero, and leave the bus for bad weather days.

Awesome that you live in such a huge sprawling city, and only really need 5 miles of range!

I just found it odd that you didn't need more everything, more range, more cargo capacity. By all means build your flyweight bike! Your distances would make just pedaling an easy option, except for the climate half the year.

I do a lot of 4 miles trips myself, but groceries are an 11 mile trip. So I have gone to longtails, and trailers. I live in the burbs, and have an equally brutal climate for biking. All the way to down town and back is 30 miles. So I had to go larger, heavier, and more battery.

dogman dan wrote: I just found it odd that you didn't need more everything, ...

Most of that is covered by the 'grocery getter'. My current project is stripping, refinishing and rebuilding an old Miyata 'six ten' frame for that purpose (it may get a trailer as well). The 'fly weight' is intended for shorter leisure trips or taking advantage of the municipal bus with the bike racks.

dogman dan wrote: ...brutal climate for biking ...

Mornings and evenings are not quite as brutal especially if one has a little assist to keep air flowing.

dogman dan wrote: Your distances would make just pedaling an easy option ...

That is why I want to be able to leave the battery off and use it in pedal only mode. For that reason I would really like to know how much drag the Bafang Mid Drive has.

I spent some time examining the the CT frame this weekend. I had failed to consider the limitations of the 'road racer' design. As it turns out I will probably be limited to 28mm wide tires. It also appears that my postage scale and manufacturer specs have a serious disagreement

Sun CR18 is a reasonable rim choice and available in 36 holes. It isn't the lightest possible rim, but they are inexpensive, very durable, build up nicely, and are 460 grams in 700C. The CR18 works well with mid-size tires like what you are considering.

You can get much nicer tires that will also be lighter. I'm using the Compass Barlow Pass on my semi-weight weenie bike at 360 grams each. They also have much lower rolling resistance than a tire like the Kenda Kourier. A major design point for my bike was reasonable weight for putting it on the bus (I have to cross a bridge that doesn't have a bike lane to get into work).

The electric components of my bike are a 8Fun/Bafang hub motor (SYXD-01F, 2kg), 15A controller from Grin, CA V3, and a Thun torque sensing bottom bracket. My current battery is an AllTech 36V/10AH, but it is too large and gives me a range of 60-70 miles. I plan on downsizing there.

I often ride my bike unpowered and there is no noticeable drag from the 8Fun hub when it isn't in use.

The torque assist is a huge part of making this bike work for me, so the Bafang mid-drive wouldn't be an option that I'd consider.

I already have the frame. As far as the 26" wheel is concerned that is why I was looking at the 650 options.But I like consistency and my other bike(s) have 700C.

I like the idea of the low power light weight cute FWD motor but I am not finding current sources for the smaller varieties.Between the weight of the a Hub Motor (QT100 ~ 2.2 KG), Controler (???), Bottom Bracket and Crank set I am almost up to the weight of the Bafang Mid Drive (if the only listed weight I have found of less than 4 KG is accurate).

Alex W wrote:Sun CR18 is a reasonable rim choice and available in 36 holes.

It is high on my short list. I think that I could use it on both bikes as well (I like consistency -- less spares to keep around).

Alex W wrote: You can get much nicer tires that will also be lighter. I'm using the Compass Barlow Pass on my semi-weight weenie bike at 360 grams each. They also have much lower rolling resistance than a tire like the Kenda Kourier.

The reason I was looking at the Kenda Kourier was for its combination of wide width(40mm) , weight, flat protection and price point. After measuring the frame this weekend the anything wider than 28 (maybe 32) is out.

If you love pedaling that frame. DONT RUIN IT with a motor. I don't recall if I mentioned it, but I have more pedal only bikes on my property than e bikes. Some of those bikes would be a shame to put a motor on. Like this one, no way a motor is going on it.

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You can still do a really nice, lighter weight, short range ebike with a tiny hub motor, and a vintage steel frame. Not hard to put 40 pounds on the bus rack.

I believe the lightest that can be done is with a friction drive. This also has the advantage of being very quick to remove, for those who care about using the bike without sometimes.

I have seen one 600w, I believe it's called add-e, that fits very neat with BB mount and weights only 2Kg including the bottle battery. One could easily build something similar, with better power or lesser weight.

A proper complete restoration is not in the cards as the decals are destroyed and replacements are unobtanium. The poper pieces parts would also be extremely expensive if one could collect them. Upgrading it to newer components is a thought. However a high end carbon crank set and new bottom bracket would cost almost a third of the price of the bafang mid drive. The mid drive and a small removable battery on the one of the water bottle mounts might make for a very aesthetically pleasing appearance. My other thought is that using a Bafang mid drive would reduce the danger of damaging those decades old aluminum dropouts.

MadRhino wrote:I believe the lightest that can be done is with a friction drive. This also has the advantage of being very quick to remove, for those who care about using the bike without sometimes.

I have seen one 600w, I believe it's called add-e, that fits very neat with BB mount and weights only 2Kg including the bottle battery. One could easily build something similar, with better power or lesser weight.

A very interesting alternative. Thank you. The price seems to be just over a thousand dollars (250 watt version). I would question the ease of building something similar without access to a good machine shop.

I have a couple of light builds that are around 30 lbs (starting with rames under 4lbs.) and do 23mph for about 24 miles.

A Q100 and a 36v10ah battery pack with Samsung 29# cells is just over 6lbs. That is how I roll.

One of them has a 47mm (700c) tire on a skinny little rim, works fine but I wouldn't want to ride it under inflated. Wide rims are great, but I wouldn't get too hung up on it.

I did buy a mint condition 20 year old 19lb lugged steel specialized race bike to put the motor on, but that bike is such a beautiful work of art and such a fine ride, I'll never put a motor on it. Specialized just did a limited edition run of my frame for $4000. Dang!http://bikeretrogrouch.blogspot.com/201 ... rsary.html

I trust that was supposed to be "one point nine" rather than "nineteen".

Nice to know the goal my goal should be obtainable. I read through the tread listed in your signature. A lot of good information there.

One thing that I have noticed is that everyone seems to so enamoured by high power and/or extended range that there are very few options for purchasing a small capacity battery. LEED does have a 24Volt 6.5AHr Panasonic battery but a small capacity 36V option seems to be DIY.

I plan on doing my own wheel builds because I want multiple gauge spokes so one item of particular interest was the source for spokes. Not for the weight savings but for the increased elasticity. I wanted matching rims on my existing bike so I ordered a spare rim from GM. The spoke holes meander around so much that it appeared to have been drilled by drunken sailor. I have built my truing stand (that can double as a test stand) and have a couple of old ARAYA 27 rims to practice on (first).

As for battery, do you have something in mind?the 29e cells have a lot of current for their size and weight. 10s4p is about 36v and 11ah and 2lbs. Paul will build you anything you want (within reason).EM3ev.com.

(P.S. the steel bike is 19 lbs complete (pedal only). I do have a 19 lb specialized Langster (the silver aluminum one) that makes a great fast like ebike).

chas58 wrote:(P.S. the steel bike is 19 lbs complete (pedal only). I do have a 19 lb specialized Langster (the silver aluminum one) that makes a great fast like ebike).

Oops ... I was thinking frame weight

chas58 wrote:As for battery, do you have something in mind? ... Paul will build you anything you want (within reason).

Well I was thinking 10s2p using Panasonic 18560B cells. If my figures are correct (20 x 46.5 grams) then that should be just over 2 pounds (plus BMS, wires, connectors, etc). This is one of the many areas I am profoundly ignorant. I do not know if the discharge rate is sufficient. The subject gets 'muddier' the more I read.

Other than cost and 0.5Ah what is the difference between the Samsung 29E and Panasonic 18560B?

I used to have sign that hung over my desk that read "Engineering is the art of planning and forethought." This is a long term project (I have to finish stripping, refinishing, rebuilding the 'grocery getter' first). The idea is to consider all the options and then have the required offshore bits shipped 'via a slow boat from China'.

on another note:In your signature thread there was a mention of using an Arduino MPU as secondary controller. At one time there was an 'open source' project to design/build an ebike motor controller. It has been several years since I read anything about it.

Alex W wrote:Sun CR18 is a reasonable rim choice and available in 36 holes.

It is high on my short list. I think that I could use it on both bikes as well (I like consistency -- less spares to keep around).

Alex W wrote: You can get much nicer tires that will also be lighter. I'm using the Compass Barlow Pass on my semi-weight weenie bike at 360 grams each. They also have much lower rolling resistance than a tire like the Kenda Kourier.

The reason I was looking at the Kenda Kourier was for its combination of wide width(40mm) , weight, flat protection and price point. After measuring the frame this weekend the anything wider than 28 (maybe 32) is out.

Wide and supple tires don't need to be flat resistant. Run them at lower pressures and you get everything -- low rolling resistance, comfortable ride, light weight, and not easily cut by glass (the wider pressure helps a lot with that).

It's not too hard to find bikes that will fit wider tires. You can also fit 38mm 650B wheels in many road frames (especially older ones) that were designed for up to 28mm 700C tires. The outside diameter is pretty similar and the conversion is easy.

I do lots of unassisted riding with the Bafang BBS02 kit, but I've only had it for 2 months. I got the kit for all the steep grades where I live, including a 4 mile 2000 foot climb to my house from anywhere. For the most part, I ride the flat unassisted.

Although I agree that any drag is not noticeable, I do think there is some based on speeds I attain on known routes that are very slight down grades. (I'm thinking the slight downgrade nullifies the weight penalty.) My speeds are typically 5-10% slower than before the kit was installed. At least that is my perception. It's hard to tell since conditions are never exactly the same, and I'm basing this on only a few rides over those spots. And because it's hard to tell, I'm quite happy with the performance unassisted.

I can feel more resistance turning the pedals by hand on the work stand than before the kit was installed. So I guess there is some. I don't know why. Shouldn't it freewheel, or not?

EstebanUno wrote:I can feel more resistance turning the pedals by hand on the work stand than before the kit was installed. So I guess there is some. I don't know why. Shouldn't it freewheel, or not?

A lot of things come into play ... that is why I asked the question. There are actually two freewheels in that setup: one for the motor and one for pedaling. You are also turning both chains anytime power is being applied (via the motor or the crank or combination). Each adds some amount of drag. Of course there is always the quality of the shaft and bearing to consider as well but this may less , more or nill depending on the crank set/bottom bracket it is being compared too.

I emailed the same question (as well a question regarding the weight) to a US Banfang Mid Drive dealer. Thus far yours is the only response that I have received. THANK YOU

As for me, born & reared, still with family. During my February visit, I made a point of getting a MetroCard and exploring the gains Houston has made towards pubic transit. And making their city bicycle friendly. Anyway, in Worcester, my goal also was to be car-free and use public transit for longer trips. Having buses with bicycle racks made that possible.

I used to have little difficulty with my Gary Fisher Gitchee with a 36V 500 watt hub motor and battery. But my latest build, a MAC 8T, OSN A123 48V on Trek Shift 3 did in fact increase the weight. I too wanted a really good wheel, and after extensive research, settled on an Alexrims DX32 with a Maxxis 2.5" Hookworm and downhill tubes. But its the 48 volt 20ah battery that added the real weight.

FYI, the Alexrims DX32 is the strongest rim they make, and an option for a MAC lace by EM3ev.com, so a good choice. And love those Maxxis Hookworms.

The weight of it now makes it difficult to lift onto the bus rack. Like others, I keep a pedal-only bicycle around, a Ross Mt. Whitney classic Chromoly frame bike in beautiful chrome. I had intended to put a motor on it, which is why I bought it, for its chromoly frame. But it was such a lovely bike and light-weight, I'm keeping it as is. And increasingly using it when I travel by bus for an errand. I can usually navigate by bus to within 2 miles of my destination and a 2 mile pedal is OK by me.

The long shot in the way of advise: 1> you seem to be on the right track, so trust your judgement, 2> get your weenie weight advantage by reducing the size of your battery, and 3> for Houston, get a really good wheel build, like can be had with a Alexrims DX32 w/Maxxis tires, or compatible.

You only need 5 miles of range, so get a battery that does that and no more. A battery in the 9-12 amp-hour range should suffice.